Dental compositions such as dental restorative materials, dental adhesives and dental cosmetic compositions are used for restoring dental cavities caused by factors such as tooth decay and caries.
In particular, dental restorative materials are essential dental materials widely utilized in a variety of applications including general dental treatments to restore sites broken by dental caries or trauma or the overall crown or to fix mobile teeth, and orthodontic or cosmetic dental treatments.
Amalgam composed of alloys and mercury has been conventionally used as dental restorative materials, but polymeric dental restorative materials (PDRMs) substitute for amalgams due to problems such as toxicity to humans and environmental pollution, and a great deal of research associated therewith has been conducted.
Since the late 1940s, a method for directly filling dental cavities with a mixture of tertiary amine-containing methacrylate monomers and benzoyl peroxide-containing polymeric powders, based on the fact that the mixture hardens at ambient temperature has been suggested. This method has been commercially available and clinically used in the U.S. since the 1950s, but was not used over a long time due to disadvantages such as transparency, high polymerization shrinkage, low color stability and hardness and lack of adhesion to teeth.
In 1951, Knock and Glenn introduced a novel restorative material and suggested a solution to the polymerization shrinkage by introducing inorganic fillers into resins. In the early 1950s, Bjorksten and Yeager introduced silane coupling agents into the surface of inorganic fillers and this method was embodied by Bowen in American National Standards Institute.
Bowen developed Bis-GMA (bisphenol A diglycidylether methacrylate) wherein methylmethacrylate is introduced into epoxy monomers in 1956 and Bis-GMA-introduced resins in 1962. In 1965, Bowen was issued a patent for a resin containing a blend of Bis-GMA with silanized quartz particles and this resin is now the most widely used dental composite.
Since the 1970s, polymeric dental restorative materials have been practically applied to dental treatments. For the early 10 years, PDRMs were used as alternatives or substitutes for silicate cement for class 3, 4 and 5 cavities. Only in the 1990s were PDRMs applied in earnest to stress-bearing molar areas, Class 1 and 2 cavities.
Such recent application is closely related to fears of patients undergoing dental treatment concerning mercury contained in dental amalgams and increased demand for aesthetic operations. Furthermore, this is due to improvement in functions of dental materials associated with these phenomena.
Unlike general materials, these dental compositions require a variety of properties due to the unique environment of the oral cavity. Specifically, dental compositions must be prepared taking into consideration various factors such as humid environments in which relative humidity is about 100%, occlusal force upon chewing, rapid temperature variation, close contact with oral soft tissues, frequent side effects such as hypersensitivity and various bacteria species present in oral cavities. Other requirements are aesthetic desires of individuals in accordance with recent development of mass media and color harmony with teeth.
In particular, anticariogenic activity to other hard tissues of teeth such as various dentins, cementum and/or enamels is considerably essential and important for dental compositions.
Accordingly, a great deal of research has been conducted to improve anticariogenic activity. For example, U.S. Pat. No. 6,326,417 discloses dental composites into which organic antibacterial materials are introduced. In addition, Japanese Patent Application Publication No. 1998-025218 discloses antibacterial fillers wherein the surface of inorganic fillers is coated with polymeric monomers including at least one antibacterial monomer. However, such an organic antibacterial agent or antibacterial filler has disadvantages of pigmentations and deteriorated physical properties.
In particular, a great deal of research associated with antibacterial and anticariogenic effects of fluorine has been conducted, and fluorine, which has been known since the early 1940s, exhibits anticariogenic activity to hard tissues of teeth and thus possesses high biological significance.
Maltz and Emilson (J Dent Res 61: 786-791) reported that fluorine at a concentration of 0.019 to 0.14 ppm exhibits inhibitory effects upon bacterial growth, and Cao et al., (J Dent Res 73. Abstr. 675) announced that when fluorine is continuously present at a concentration as low as 0.01 ppm, it is effective for recalcification of various lesions and inhibition of caries. In addition, Attin et al., (Clin Oral Invest 11: 83-88) reported that fluorine at a concentration of 0.04 ppm inhibits various growth.
In vitro research has demonstrated that, as depicted in the following reaction scheme, fluorine is chemically bonded to hydroxyapatite of tooth substrates to form antiacidic fluoroapatite, reinforcing teeth. In addition, fluorine inhibits formation of glucane by glucose transferase in the process of bacterial metabolism in oral cavities.Ca10(PO4)6(OH)2+2F−→Ca10(PO4)6F2+2OH−  (1)
Accordingly, introduction of fluorine into dental materials inhibits decalcification of teeth and improves recalcification thereof, thereby advantageously inhibiting production of carbohydrates and formation of tartar by bacteria fermentation. That is, fluorine also reinforces teeth, thus performing an important major function for designing materials imparting permanence to adhesion to dentine.
Meanwhile, of dental composition ingredients, polymeric resins disadvantageously shrink upon polymerization, thus providing a space between teeth and restorative materials and leading to a micro-leakage. In this case, bacteria may permeate the space provided between teeth and restorative materials, inducing secondary caries. Accordingly, whether or not anticariogenic activity is exerted is a considerably important issue.
Accordingly, in an attempt to prevent secondary caries caused by polymeric resins, research associated with fluoride-containing dental restorative materials wherein a tooth substrate constituting cavity walls is fluoridized with fluoride ions released from fluoride in order to reinforce the tooth substrate has been conducted.
For example, U.S. Pat. No. 6,703,518 discloses research associated with fluorine-releasing compositions. This patent also discloses research associated with fluorine-releasing materials such as fluorine-releasing copolymers, fluoroaluminosilicate glasses, metal fluorides and ammonium fluorides.
Application of these technologies is limited due to problems such as considerably low fluoride ion release level, deterioration in mechanical properties upon fluorine release and undesired release behaviors of fluoride ions wherein the fluoride ions are rapidly released only in an initial stage, but release thereof gradually decreases.
Accordingly, there is an urgently increasing need for technology development associated with dental compositions, i.e., dental restorative materials that exhibit superior mechanical properties and aesthetic effects and continuously exert uniform anticariogenic activity so as to inhibit or prevent decay of hard tissues of teeth.